JP2012020642A - Pneumatic tire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pneumatic tire that improves separation-resistance of a bead part while preventing deterioration in operation stability.SOLUTION: In the pneumatic tire provided with a bead core, a carcass layer folded back around the bead core, and a bead filler arranged outside the bead core in a tire radial direction. The carcass layer includes a folded portion folded back around the bead core, and a carcass body part located inside the folded portion in a tire rotational axis direction. The bead filler includes: a lower bead filler covering the outer surface of the bead core in the tire radial direction, and becoming thinner away from the bead core; and an upper bead filler arranged between the lower bead filler and the carcass body part and between the lower bead filler and the folded part so as to hold the lower bead filler therebetween, and having a smaller modulus than the lower bead filler when being extended 100%.

Description

  The present invention relates to a heavy duty pneumatic tire used for trucks and buses.

  In heavy-duty pneumatic tires used for trucks and buses, the carcass layer is folded around the bead core from the inside to the outside in the tire rotation axis direction, and the tread from the bead core is between the carcass main body and the folded portion of the carcass layer. A bead filler extending so as to taper toward the side is disposed. A bead filler is comprised from the rubber composition with comparatively high hardness, and mainly contributes to the improvement of steering stability.

  When a load is applied to the pneumatic tire, the sidewall portion usually bends. However, when an extremely large load is applied to the pneumatic tire, not only the sidewall portion is bent, but also the bead portion including the bead filler falls down outward in the tire rotation axis direction with the rim flange as a fulcrum. Therefore, when a pneumatic tire is used under severe load conditions, a large compressive strain or compressive stress is generated in the bead portion, which may cause a separation failure.

  Conventionally, a pneumatic tire is known in which a strain-reducing rubber layer that is harder than the coat rubber of the carcass layer but softer than the hardest part of the bead filler is interposed between the carcass main body and the bead filler (Patent Document 1). .

JP 2008-307949 A

  However, the conventional pneumatic tire described above cannot sufficiently suppress a separation failure that occurs in the bead portion when used under severe load conditions.

  An object of this invention is to provide the pneumatic tire which can improve the separation resistance of a bead part, suppressing the fall of steering stability.

  A pneumatic tire according to the present invention is a pneumatic tire comprising a bead core, a carcass layer folded around the bead core, and a bead filler disposed on a radially outer side of the bead core. The layer includes a folded portion that is folded around the bead core, and a carcass main body portion that is located inward in the tire rotation axis direction relative to the folded portion, and the bead filler is disposed on the outer side in the tire radial direction of the bead core. A lower bead filler that covers a surface and decreases in thickness as it moves away from the bead core; and the lower bead filler and the carcass body so as to sandwich the lower bead filler; and the lower bead It is arranged between the filler and the folded portion, and has a modulus at 100% elongation smaller than that of the lower bead filler. An upper bead filler have, characterized in that it comprises a.

  Further, the thickness of the lower bead filler is the thickness of the bead filler on a straight line passing through the midpoint between the outer end of the bead core in the tire radial direction and the end of the folded portion and parallel to the tire rotation axis. Of the upper bead filler, and the thickness of the portion between the lower bead filler and the carcass main body is 5% or more of the thickness of the bead filler. Of the fillers, the thickness of the portion between the lower bead filler and the folded portion is preferably 5% or more of the thickness of the bead filler.

  Moreover, it is preferable that the thickness of the lower bead filler is 20% or less of the thickness of the bead filler on a straight line passing through the end of the folded portion and parallel to the tire rotation axis.

  The modulus at 100% elongation of the lower bead filler is preferably 13.0 MPa or more.

  The modulus at 100% elongation of the upper bead filler is preferably 1.5 MPa or more and 3.0 MPa or less.

  The upper bead filler includes an inner bead filler disposed between the lower bead filler and the carcass main body, and an outer bead filler disposed between the lower bead filler and the folded portion. The modulus of 100% elongation of the inner bead filler is preferably smaller than the modulus of 100% elongation of the outer bead filler.

  The modulus at 100% elongation of the inner bead filler is preferably 1.5 MPa to 2.5 MPa, and the modulus at 100% elongation of the outer bead filler is preferably 2.0 MPa to 3.0 MPa. .

  Moreover, it is preferable that the thickness of the inner bead filler is smaller than the thickness of the outer bead filler on a straight line passing through the end of the folded portion and parallel to the tire rotation axis.

  According to the pneumatic tire of the present invention, it is possible to improve the separation resistance of the bead portion while suppressing a decrease in steering stability.

It is a half sectional view showing an example of a pneumatic tire of an embodiment. It is the figure which expanded the bead part of the pneumatic tire of an embodiment. It is the figure which expanded the bead part of the pneumatic tire of an embodiment. It is the figure which expanded the bead part of the pneumatic tire of the prior art example.

<First Embodiment>
Hereinafter, the pneumatic tire of the present invention is explained based on an embodiment. The pneumatic tire of the embodiment described below can be applied to heavy duty tires for trucks and buses defined in Chapter C of JATMA YEAR BOOK 2009 (Japan Automobile Tire Association Standard).

  In the following description, the tire rotation axis direction is a direction parallel to the rotation axis of the pneumatic tire. Further, the outward direction of the tire rotation axis is a direction away from the tire equator line CL in the tire rotation axis direction. Further, the inner side in the tire rotation axis direction is a direction approaching the tire equator line CL in the tire rotation axis direction. The tire radial direction is a direction orthogonal to the rotation axis of the pneumatic tire. The outer side in the tire radial direction is a side away from the rotation axis of the pneumatic tire in the tire radial direction.

  First, a schematic configuration of the pneumatic tire of the present embodiment will be described with reference to FIG. FIG. 1 is a half sectional view showing an example of the pneumatic tire of the present embodiment. As shown in FIG. 1, the pneumatic tire of this embodiment includes a tread portion 10, a sidewall portion 20, a bead portion 30, a belt layer 50, and a carcass layer 60. As shown in FIG. 1, the pneumatic tire is mounted on a rim 80.

  As shown in FIG. 1, the sidewall portion 20 includes a side rubber layer 22. The bead unit 30 includes a bead core 32, a lower bead filler 34, and an upper bead filler 36. The cross-sectional shape of the bead core 32 of this embodiment is a hexagon. Further, around the bead core 32, a carcass layer 60 is folded back from the inner side in the tire rotation axis direction toward the outer side in the tire rotation axis direction. Here, a portion of the carcass layer 60 that is not folded back by the bead core 32 is defined as a carcass body portion 62, and a portion that is folded by the bead core 32 is defined as a folded portion 64.

A carcass reinforcing layer 66 is provided along the carcass layer 60. The carcass reinforcing layer 66 includes a steel cord.
Further, carcass reinforcing layers 68 and 70 are provided between the carcass layer 60 and the sidewall rubber layer 22. The carcass reinforcing layers 68 and 70 include nylon cords.
The bead portion 30 is provided with a rim cushion rubber layer 72. The rim cushion rubber layer 72 is in direct contact with the rim 80.

Here, with reference to FIG. 2, the structure of the bead part 30 of this embodiment is demonstrated in detail. FIG. 2 is an enlarged view of the bead portion 30 of the pneumatic tire of the present embodiment. As shown in FIG. 2, the lower bead filler 34 covers the upper portion of the bead core 32 (the surface on the outer side in the tire radial direction). Further, as the distance from the bead core 32 increases, the thickness of the lower bead filler 34 decreases.
Here, the modulus at 100% elongation of the lower bead filler 34 is preferably 13.0 MPa or more. By setting the modulus at the time of 100% elongation of the lower bead filler 34 to 13.0 MPa or more, the steering stability can be improved. Further, the modulus at 100% elongation of the lower bead filler 34 is preferably 18.0 MPa or less. The 100% modulus is a value measured according to JIS K 6250.

  Further, the upper bead filler 36 is disposed between the lower bead filler 34 and the carcass main body 62 and between the lower bead filler 34 and the folded portion 64 so as to sandwich the lower bead filler 34. . Further, the modulus at 100% elongation of the upper bead filler 36 is smaller than the modulus at 100% elongation of the lower bead filler 34. For example, the modulus at 100% elongation of the upper bead filler 36 is 1.5 MPa or more and 3.0 MPa or less.

Here, in general, in order to improve the handling stability, it is preferable to increase the modulus at 100% elongation of the lower bead filler 34. However, when the lower bead filler 34 having a large modulus at 100% elongation comes into contact with the carcass layer 60, the difference in rigidity increases, cracks are generated between the lower bead filler 34 and the carcass layer 60, and the beads 30 are separated. Is likely to occur.
On the other hand, the pneumatic tire according to the present embodiment is provided between the lower bead filler 34 and the carcass main body 62 and between the lower bead filler 34 and the folded portion 64 so as to sandwich the lower bead filler 34. An upper bead filler 36 having a modulus that is 100% smaller than that of the lower bead filler 34 is disposed therebetween. Therefore, the lower bead filler 34 can be prevented from coming into contact with the carcass layer 60. As a result, according to the pneumatic tire of the present embodiment, it is possible to improve the separation resistance of the bead portion while suppressing a decrease in steering stability.

Hereinafter, more specific shapes of the lower bead filler 34 and the upper bead filler 36 will be described. First, through the upper end of the bead core 32 (the tire radial direction outer end), to define a line parallel with the tire rotation axis L _1. In addition, as the upper end of the folded portion 64, to define a line parallel with the tire rotation axis L _2. In addition, as the midpoint between the upper ends of the folded portion 64 of the bead core 32, define a line parallel with the tire rotation axis L _3.
Further, the thickness of the lower bead filler 34 on the straight line L ₃ is defined as t _1. Also, of the upper bead filler 36 on the straight line L _3, to define the thickness of the portion between the lower bead filler 34 and the carcass main body portion 62 and t _2. Also, of the upper bead filler 36 on the straight line L _3, to define the thickness of the portion between the folded portion 64 and the lower bead filler 34 and t _3. Further, the thickness of the bead filler on the straight line L ₃ is defined as T _1. Here, T ₁ is equal to the sum of t ₁ , t ₂ and t ₃ .

On the straight line L ₃ , the thickness t ₁ of the lower bead filler 34 is preferably 40% or more of the thickness T ₁ of the bead filler. By setting the thickness t ₁ of the lower bead filler 34 to 40% or more of the thickness T ₁ of the bead filler, it is possible to suppress a decrease in steering stability.
Further, on the straight line L _3, of the upper bead filler 36, the thickness t ₂ of the portion between the lower bead filler 34 and the carcass main body portion 62 is 5% or more of the bead filler thickness T ₁ It is preferable. The t ₂ by 5% or more of T _1, it is possible to suppress the occurrence of cracks between the lower bead filler 34 and the carcass main body portion 62, to improve the separation resistance of the bead portion.
Further, it on the straight line L _3, of the upper bead filler 36, the thickness t ₃ of the portion between the folded portion 64 and the lower bead filler 34 is 5% or more of the bead filler thickness T ₁ Is preferred. By setting t ₃ to 5% or more of T ₁ , it is possible to suppress the occurrence of cracks between the lower bead filler 34 and the folded portion 64 and to improve the separation resistance of the bead portion.

Further, on the straight line _{L 2,} we define the thickness of the lower bead filler 34 and _{t 4.} Further, the thickness of the bead filler on the straight line L ₂ is defined as T _2. On the straight line _{L 2,} the thickness _{t 4} of the lower bead filler 34 is preferably 20% or less of the thickness _{T 2} of the bead filler. For example, in the present embodiment, the thickness t ₄ of the lower bead filler 34 is 10% of the thickness T ₂ of the bead filler.
As the thickness t ₄ of the lower bead filler 34 becomes 20% or less of the thickness T ₂ of the bead filler on the straight line L ₂ , the lower bead filler 34 gradually becomes thinner as it moves away from the bead core 32. Separation at the end of the carcass can be suppressed.

  As described above, according to the pneumatic tire of the present embodiment, it is possible to improve the separation resistance of the bead part while suppressing a decrease in steering stability.

<Second Embodiment>
Next, the configuration of the pneumatic tire according to the second embodiment will be described. The basic configuration of the pneumatic tire of the present embodiment is the same as that of the embodiment described with reference to FIG. In the present embodiment, the configuration of the upper bead filler 36 is different from that of the first embodiment. Hereinafter, the description of the same part as 1st Embodiment is abbreviate | omitted, and a different part from 1st Embodiment is demonstrated.

  With reference to FIG. 3, the structure of the upper bead filler 36 of this embodiment is demonstrated. FIG. 3 is an enlarged view of the bead portion 30 of the pneumatic tire of the present embodiment. As shown in FIG. 3, the upper bead filler 36 of this embodiment includes an inner bead filler 38 and an outer bead filler 40. The inner bead filler 38 is disposed between the lower bead filler 34 and the carcass main body 62. The outer bead filler 40 is disposed between the lower bead filler 34 and the folded portion 64. The inner bead filler 38 and the outer bead filler 40 are in contact with each other on the outer side in the tire radial direction than the lower bead filler 34.

The modulus at 100% elongation of the inner bead filler 38 is smaller than the modulus at 100% elongation of the outer bead filler 40. For example, the modulus at 100% elongation of the inner bead filler 38 is 1.5 MPa or more and 2.5 MPa or less. Further, the modulus at 100% elongation of the outer bead filler 40 is 2.0 MPa or more and 3.0 MPa or less.
In addition, as the upper end of the folded portion 64, in the tire rotation axis parallel to the straight line L _2, the thickness of the inner bead filler 38 is preferably thinner than the thickness of the outer bead filler 40.

  The upper bead filler 36 of the pneumatic tire of the present embodiment includes an inner bead filler 38 and an outer bead filler 40. Further, the modulus at 100% elongation of the inner bead filler 38 is smaller than the modulus at 100% elongation of the outer bead filler 40. Therefore, according to the pneumatic tire of the present embodiment, it is possible to further improve the separation resistance of the bead portion while suppressing a decrease in steering stability.

  The test which confirms the effect of this invention was done using the various pneumatic tires. The tire size was 295 / 80R22.5, and the air pressure conditions defined in JATMA YEAR BOOK 2009 (Japan Automobile Tire Association Standard) were used. Each test tire was mounted on a 2-D vehicle, and the following test was performed.

(Maneuvering stability)
Each test tire was mounted on all wheels of a 2-D vehicle, and a sensory test was conducted by a test driver on a test course under the maximum load condition defined in JATMA YEAR BOOK 2009. An evaluation result is shown by an index value where the conventional example is 100. The larger this value, the better the steering stability. In addition, when the index value was 90 or more, it was judged that the fall of steering stability could be suppressed.

(Separation resistance)
Each test tire was mounted on the rear wheel of a 2-D vehicle, and after running for 50,000 km under the condition of 120% of the maximum load specified in JATMA YEAR BOOK 2009, the occurrence of bead separation was examined. .
Further, the drum endurance test was conducted for 10,000 km under the condition of 160% of the maximum load of JATMA, and then the presence or absence of bead separation was examined.

(Conventional example, Examples 1 to 6)
Using the pneumatic tires of the conventional example and Examples 1 to 6, the lower bead filler 34 and the carcass main body 62 out of the thickness t ₁ of the lower bead filler 34 on the straight line L ₃ and the upper bead filler 36 the thickness t ₂ of the portion _between, among the upper bead filler 36, examined the effect of varying the thickness t ₃ of the portion between the folded portion 64 and the lower bead filler 34.

  First, a conventional pneumatic tire will be described. The basic configuration of the conventional pneumatic tire is the same as that of the first embodiment described with reference to FIG. The conventional pneumatic tire is different from the first embodiment in the configuration of the lower bead filler 34 and the upper bead filler 36. Hereinafter, the lower bead filler 34 and the upper bead filler 36 in the conventional example will be described with reference to FIG.

FIG. 4 is an enlarged view of a bead portion 30 of a conventional pneumatic tire. As shown in FIG. 4, the lower bead filler 34 of the conventional example covers the upper part of the bead core 32. In addition, the lower bead filler 34 in the conventional example is in contact with the carcass main body 62, and the thickness of the lower bead filler 34 decreases as the distance from the bead core 32 increases.
The conventional upper bead filler 36 is disposed between the lower bead filler 34 and the folded portion 64.

Moreover, the schematic structure of the pneumatic tire of each Example is the same as that of 1st Embodiment demonstrated with reference to FIG. 1, FIG. In the pneumatic tires of Examples 1 to 6, the thickness t ₁ of the lower bead filler 34 on the straight line L ₃ and the portion between the lower bead filler 34 and the carcass main body portion 62 among the upper bead filler 36. Of the thickness t ₂ and the upper bead filler 36, the thickness t ₃ of the portion between the lower bead filler 34 and the folded portion 64 is different from each other.
The t ₁ / T ₁ , t ₂ / T ₁ , and t ₃ / T ₁ of the pneumatic tires of the conventional example and Examples 1 to 6 are as shown in Table 1 below.

The thickness t ₄ of the lower bead filler 34 on the straight line L _{2 of the} conventional example and the pneumatic tires of Examples 1 to 6 is 10% of the bead filler thickness T ₂ .
The modulus at 100% elongation of the lower bead filler 34 of the pneumatic tires of the conventional example and Examples 1 to 6 is 13.0 MPa in all cases. In addition, the modulus at 100% elongation of the upper bead filler 36 of each of the pneumatic tires of the conventional example and Examples 1 to 6 is 2.0 MPa.

Table 1 shows the test results of steering stability and separation resistance in the conventional example and Examples 1 to 6.

As shown in Table 1, in the pneumatic tires of Examples 1 to 6, the lower bead filler 34 and the lower bead filler 34 are interposed between the lower bead filler 34 and the carcass main body 62 so as to sandwich the lower bead filler 34. Since the upper bead filler 36 having a modulus that is 100% smaller than that of the lower bead filler 34 is disposed between the lower bead filler 34 and the folded portion 64, the separation resistance of the bead portion is reduced while suppressing a decrease in steering stability. It has been found that it can be improved.
Further, it has been found that the steering stability is improved by setting the thickness t ₁ of the lower bead filler 34 to 40% or more of the thickness T ₁ of the bead filler.

(Conventional example, Examples 4, 7, and 8)
Using the pneumatic tires of the conventional example and Examples 4, 7, and 8, the effect of changing the modulus at 100% elongation of the lower bead filler 34 was examined.
The t ₁ / T ₁ , t ₂ / T ₁ , and t ₃ / T ₁ of the pneumatic tires of the conventional example and Examples 4, 7, and 8 are as shown in Table 2 below. In addition, the thickness t ₄ of the lower bead filler 34 on the straight line L ₂ of the pneumatic tires of the conventional examples and Examples 4, 7, and 8 is 10% of the thickness T ₂ of the bead filler. Further, the modulus at 100% elongation of the upper bead filler 36 of the pneumatic tire of each of the conventional examples and Examples 4, 7, and 8 is 2.0 MPa.

The modulus at 100% elongation of the lower bead filler 34 of the pneumatic tire of the conventional example is 13.0 MPa.
The modulus at 100% elongation of the lower bead filler 34 of the pneumatic tire of Example 7 is 12.0 MPa.
The modulus at 100% elongation of the lower bead filler 34 of the pneumatic tire of Example 7 is 13.0 MPa.
The modulus at 100% elongation of the lower bead filler 34 of the pneumatic tire of Example 7 is 13.5 MPa.

Table 2 shows the test results of steering stability and separation resistance in the conventional example and Examples 4, 7, and 8.

  As shown in Table 2, it was found that when the modulus at 100% elongation of the lower bead filler 34 is 13.0 MPa or more, the steering stability is improved.

(Conventional example, Examples 4 and 9)
Using the pneumatic tires of the conventional example and Examples 4 and 9, the effect of the upper bead filler 36 including the inner bead filler 38 and the outer bead filler 40 was examined.
The schematic configuration of the pneumatic tire of Example 9 is the same as that of the second embodiment described with reference to FIGS. 1 and 3.
The t ₁ / T ₁ , t ₂ / T ₁ , and t ₃ / T ₁ of the conventional pneumatic tires of Examples 4 and 9 are as shown in Table 3 below.

The thickness t ₄ of the lower bead filler 34 on the straight line L ₂ of the pneumatic tires of the conventional example and Examples 4 and 9 is 10% of the bead filler thickness T ₂ .
The modulus at 100% elongation of the lower bead filler 34 of the pneumatic tires of the conventional examples and Examples 4 and 9 is 13.0 MPa in all cases.
Further, the modulus at 100% elongation of the upper bead filler 36 of the pneumatic tire of the conventional example and Example 4 is both 2.0 MPa. The modulus at 100% elongation of the inner bead filler 38 of the pneumatic tire of Example 9 is 2.0 MPa. Further, the modulus at 100% elongation of the outer bead filler 40 of the pneumatic tire of Example 9 is 2.6 MPa.

Table 3 shows the test results of steering stability and separation resistance in the conventional example and Examples 4 and 9.

  As shown in Table 3, in Example 9 in which the upper bead filler 36 includes the inner bead filler 38 and the outer bead filler 40, no bead separation occurred even after the drum durability test. For this reason, it has been found that the separation resistance of the bead portion is further improved when the upper bead filler 36 includes the inner bead filler 38 and the outer bead filler 40.

  From the results shown in Tables 1 to 3, it was found that according to the pneumatic tire of the present invention, it is possible to improve the separation resistance of the bead portion while suppressing a decrease in steering stability.

  As mentioned above, although the pneumatic tire of this invention was demonstrated in detail, this invention is not limited to the said embodiment. It goes without saying that various improvements and modifications may be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 10 Tread part 20 Side wall part 22 Side rubber layer 30 Bead part 32 Bead core 34 Lower bead filler 36 Upper bead filler 38 Inner bead filler 40 Outer bead filler 50 Belt layer 60 Carcass layer 62 Carcass main body part 64 Folding parts 66, 68, 70 Carcass reinforcement layer 72 Rim cushion rubber layer 80 Rim

Claims (8)

A bead core,
A carcass layer folded around the bead core;
A pneumatic tire comprising a bead filler disposed on the outer side in the tire radial direction than the bead core,
The carcass layer is
A folded portion folded around the bead core;
A carcass main body located on the inner side in the tire rotation axis direction than the folded portion, and
The bead filler is
A lower bead filler that covers the outer surface of the bead core in the tire radial direction and has a thickness that decreases with distance from the bead core;
The lower bead filler is disposed between the lower bead filler and the carcass main body and between the lower bead filler and the folded portion so as to sandwich the lower bead filler. Upper bead filler with a low modulus at% elongation,
A pneumatic tire characterized by comprising: Through a midpoint between the end of the bead core in the tire radial direction and the end of the folded portion, on a straight line parallel to the tire rotation axis,
The thickness of the lower bead filler is 40% or more of the thickness of the bead filler,
Of the upper bead filler, the thickness of the portion between the lower bead filler and the carcass main body is 5% or more of the thickness of the bead filler,
2. The pneumatic tire according to claim 1, wherein a thickness of a portion between the lower bead filler and the folded portion of the upper bead filler is 5% or more of a thickness of the bead filler. On the straight line passing through the end of the folded portion and parallel to the tire rotation axis,
The pneumatic tire according to claim 1 or 2, wherein the thickness of the lower bead filler is 20% or less of the thickness of the bead filler.   The pneumatic tire according to any one of claims 1 to 3, wherein a modulus at 100% elongation of the lower bead filler is 13.0 MPa or more.   The pneumatic tire according to any one of claims 1 to 4, wherein a modulus at 100% elongation of the upper bead filler is 1.5 MPa or more and 3.0 MPa or less. The upper bead filler is
An inner bead filler disposed between the lower bead filler and the carcass body,
An outer bead filler disposed between the lower bead filler and the folded portion;
With
The pneumatic tire according to any one of claims 1 to 5, wherein a modulus at 100% elongation of the inner bead filler is smaller than a modulus at 100% elongation of the outer bead filler. The modulus at 100% elongation of the inner bead filler is 1.5 MPa or more and 2.5 MPa or less,
The pneumatic tire according to claim 6, wherein a modulus at 100% elongation of the outer bead filler is 2.0 MPa or more and 3.0 MPa or less. On the straight line passing through the end of the folded portion and parallel to the tire rotation axis,
The pneumatic tire according to claim 6 or 7, wherein a thickness of the inner bead filler is thinner than a thickness of the outer bead filler.